1. Field of the Invention
The present invention relates to an inclination adjusting device for adjusting the inclination of an objective lens or the like, disposed in an optical information recording and reproduction apparatus in which information is optically recorded, reproduced, or deleted by the radiation of light beams to a recording medium.
2. Description of the Prior Art
FIG. 9 shows an optical pickup used for an optical recording and reproduction apparatus. The optical pickup comprises an optical head 3 which is disposed opposite to an optical disk 1 rotating around a vertical axis with a motor 1a, so as to radiate light beams 2 to a recording medium 1b on the optical disk 1. The optical head 3 includes a laser light source 4 for emitting the light beams 2 in the horizontal direction, a mirror 5 for reflecting the light beams 2 at an angle of 90 degree to direct them to the optical disk 1, and an objective lens 7 for converging the reflected light beams 2 to a spot on the recording medium 1b of the optical disk 1. The optical head 3 also includes a linear motor 6 which allows the optical head 3 to move in the tracking directions shown by a double arrow A. When the optical disk 1 is a magneto-optic disk, a coil 1c for applying a magnetic field to the disk is disposed opposite to the optical head 3 across the disk.
In the pickup having the structure described above, in order to record or reproduce information with high precision, the recording medium 1b of the optical disk 1 must receive the light beams 2 vertically. If the objective lens 7 is disposed with an inclination against the direction of the light beams 2, aberration occurs for the light beams 2 directing from the objective lens 7 to the optical disk 1. As a result, the light beams 2 are not correctly converged onto the right track on the optical disk 1, but adjacent tracks are also irradiated. This causes an Airy ring (second maximum) of the light beams 2 as well as cross talk. To prevent these troubles, the optical pickup is provided with an inclination adjusting device 8 for the objective lens 7 so that the light beams 2 can be focused onto the right track on the optical disk 1.
As shown in FIG. 10, the inclination adjusting device 108 for the objective lens 7 comprises a base 120 and an adjusting bed 110. The base 120 provides a level for the adjustment of the inclination of an objective lens 7. The adjusting bed 110 holds the objective lens 7 therein, and is supported on the base 120 in a manner that it can tilt against the base 120. The inclination of the objective lens 7 is corrected by adjusting the angle of the inclination of the adjusting bed 110 against the base 120.
The base 120 comprises a pair of support portions 123 appropriately spaced apart from each other on one side and a flat connecting portion 122 on the other side through which the support portions 123 are connected. A pair of magnetic circuits 121 are mounted on the connecting portion 122. The magnetic circuits 121 are appropriately spaced apart from the support portions 123, respectively. The support portions 123 extend upward beyond the height of the connecting portion 122, and the upper portions of the support portions 123 extend horizontally toward each other to form seat portions 123a, respectively. A fixing stand 129 protruding upward is disposed on a portion of one of the seat portions 123a close to the magnetic circuit 121. The fixing stand 129 has a threaded hole 129a in the top surface thereof, into which the bottom portion of a fixing screw 135 described hereafter is screwed.
A cylindrical positioning recess 126 is formed adjacent to the fixing stand 129 on the same seat portion 123a, and receives part of the lower portion of a steel ball 140 as a support. One of through holes 124 is vertically formed through the same seat portion 123a at a position apart from the magnetic circuit 121 with regard to the positioning recess 126, and a first adjusting screw 130a is inserted through the through hole 124 from the bottom thereof. The other through hole 124 is vertically formed through the other seat portion 123a at a position close to the magnetic circuit 121, and a second adjusting screw 130b is inserted through the through hole 124 from the bottom thereof. Pin receiving recesses 125 are formed on the center portions of the seat portions 123a, respectively. The pin receiving recesses 125 receive the lower portions of guide pins 132, supporting the guide pins 132 to stand vertically.
The adjusting bed 110 comprises a flat adjusting board 113 which is supported on the seat portions 123a. Upward and downward protrusions 113a are formed on the center side portion of the adjusting board 113 apart from the magnetic circuits 121 so that they are positioned in the space between the seat portions 123a. End portions of plate springs 112 are attached to the top surface and the bottom surface of the upward and downward protrusions 113a, respectively. The plate springs 112 horizontally extend toward the magnetic circuits 121. A lens holder 111 is attached to the ends, and the objective lens 7 is held in the center portion of the lens holder 111.
Two half portions of the adjusting board 113 separated by the protrusions 113a are put on the seat portions 123a, respectively. A cylindrical recess 116 is formed in the bottom surface of one half portion of the adjusting board 113 so as to correspond to the positioning recess 126 formed in one of the seat portions 123a. The recess 116 receives part of the upper portion of the steel ball 140. The adjusting board 113 is supported in a manner that it can tilt against the seat portions 123a on the steel ball 140.
Threaded through holes 114 are formed through the two half portions of the adjusting board 113 so as to correspond to the through holes 124 formed through the seat portions 123a, respectively. The first and second adjusting screws 130a and 130b which have been inserted through the through holes 124 are screwed through the threaded through holes 114, respectively. The first and second adjusting screws 130a and 130b are positioned on the axis x and the axis y, respectively, on the x-y coordinate with the position of the steel ball 140 as the origin. The first and second adjusting screws 130a and 130b also extend through coil springs 131 which are interposed between the adjusting board 113 and the seat portions 123a, respectively, in their compressed state.
Pin through holes 115 are formed through the two half portions of the adjusting board 113 for allowing the guide pins 132 vertically supported by the pin receiving recesses 125 in the seat portions 123a to extend therethrough, respectively. The adjusting board 113 is set in a proper position with regard to the seat portions 123a of the base 120 by the guide pins 132 which are disposed opposite to each other across the plate springs 112 and movable inside the pin through holes 115.
A pressing plate 134 extends over one half portion of the adjusting board 113 in parallel therewith with one end portion thereof fixed to the top surface of the fixing stand 129. The end portion of the pressing plate 134 has a through hole 134b through which the fixing screw 135 is inserted. The fixing screw 135 is then screwed into the threaded hole 129a of the fixing stand 129. The other end portion of the pressing plate 134 which is free to bend upward and downward, has a hemispherical downward projection 134a formed on the bottom surface thereof. The bottom end of the projection 134a presses a portion on the adjusting board 113 right above the steel ball 140.
The inclination adjusting device for an objective lens having the above-described structure is operated as follows.
The adjusting board 113 is supported tiltably against the seat portions 123a on the steel ball 140 fitted in the positioning recess 126 formed on one of the seat portions 123a. Under the above condition, by turning the first or second adjusting screw 130a or 130b, the adjusting board 113 tilts against the seat portions 123a on the steel ball 140 serving as a support. When the first adjusting screw 130a is turned, an inclination of the adjusting board 113 in the longitudinal direction of the plate springs 112 is adjusted. As a result, the inclination of the objective lens 7 held in the end portion of the plate springs 112 in this direction is also adjusted. When the second adjusting screw 130b is turned, an inclination of the adjusting board 113 in the direction crossing the longitudinal direction of the plate springs 112 is adjusted. As a result, the inclination of the objective lens 7 in this direction is also adjusted. In this way, the inclination of the objective lens 7 against the horizontal level is adjusted, so that the light beams passing through the objective lens 7 are converged onto a spot of the recording medium of the optical disk.
In the above-described device, the pair of guide pins 132 extend through the adjusting board 113, respectively, in a manner that they are slidable inside the through holes. Thus, the adjusting board 113 can tilt smoothly along the guide pins 132. However, the adjusting board 113 and the seat portions 123a must be large enough to accommodate these guide pins. Also, the weight is increased by including two guide pins.